Flashcards

AS DT Revision

Aidan Magee English 200 cards

Cards in this deck (200)

1PlasticityThe ability of a material to return to its original shape once the deforming force has been removed.
2DuctilityThe ability of a material to be drawn or stretched.
3HardnessThe ability of a material to withstand indentation, abrasion or scratching.
4BrittlenessThe tendency of a material to fracture under stress.
5MalleabilityThe ability of a metal to be deformed by compression without being torn or cracked.
6Aesthetic propertiesThe sensory qualities of a material.
7Functional propertiesThe qualities a material must possess in order to be fit for purpose, for example the correct weight, size, etc.
8Mechanical propertiesA material's reaction to physical forces, e.g. strength, plasticity, ductility, hardness, brittleness, malleability, etc
9Ferrous• Metals that contain mainly ferrite or iron, such as steel which is made up of iron with various amounts of carbon.
• Occasionally ferrous metals have small amounts of other substances added to them to enhance their properties.
• Ferrous metals will rust and all are magnetic.
10Non-ferrous• Metals which contain no iron, such as aluminium, tin and copper.
• Non-ferrous metals do not rust, and they are not magnetic.
11Alloys• Metals that have been formed by mixing two or more metals and occasionally other elements in order to produce metals with enhanced properties.
12Ferrous MetalsWhite cast iron
Grey cast iron
Mild steel
Medium Carbon steel
High carbon steels
13Non-ferrous metalsAluminium
Copper
Zinc
14AlloysStainless steel
Duralumin
Brass
15White cast iron• Hard
• Brittle
• Not an easy material to work
• Cannot be machined
• 1.7-2.9% carbon content
16Advantages of Grey cast iron• Grey cast iron is the most useful.
• Can be cast into intricate shapes
• Often used for components on machines such as the tail stocks on lathes.
• Can be machined
• When compared to steel it is relatively corrosion resistant.
• 2.5-4% carbon content
17Disadvantages of Grey cast iron• One downside of cast iron is that it is brittle
• It will shatter, or break, if dropped
• It is almost impossible to weld.
• lt has high thermal conductivity which makes it ideal in situations where heat might be an issue. Examples of its use are in cookware and in braking systems in cars.
18Advantages of Mild steel• Steel is alloy of iron and carbon.
• The more carbon added harder
• Mild steel has a carbon content of between 0.15 and 0.30 per cent.
• Ductile
• Malleable
• Tough
• Hard
• lt is easily worked; it can be cut, machined, heated and hammered into shape.
• However, apart from case hardening, mild steel cannot be heat treated.
19Disadvantages of Mild steel• One major problem that steel does have is that it rusts.
• The iron in the steel reacts with oxygen in the air and oxidation begins to take place and this can be a problem.
20Medium Carbon steel• 0.30 – 0.70% carbon content
• Harder than mild steel
• Less ductile
• Less malleable
• Used for garden tools and springs
21High carbon steels• 0.70 - 1.40% carbon content
• Properties can be improved by heat treating
• These are used in products that need to be much harder like hammer heads, cutting tools and drills.
• Carbon steel is very versatile material. it can be cut, shaped and machined.
• The main disadvantage of carbon steel is that because it is a ferrous metal, it is prone to rusting. To prevent rusting, carbon steel should be painted or galvanised.
22Stopping Oxidation• In order to stop oxidation, a barrier needs to be put between the steel and the atmosphere and the easiest way to do this is to paint the steel. This stops the oxygen in the atmosphere getting to the metal.
• Another method of preventing oxidation in steel is galvanisation, where a layer of zinc is put over the steel or plastic coating where a thermoplastic is melted over the steel.
23Advantages of Aluminium• Aluminium is a pure metal.
• It is soft and malleable and conducts heat and electricity well.
• However, in its purest form, it is useless as an engineering material
• Is always alloyed to improve its properties.
• Extremely lightweight. For this reason it is a material that is extensively used in the aircraft industry.
• Generally weather resistant
• Does not require a surface finish
• Tough
• Recyclable
24Disadvantages of Aluminium• Aluminium will polish up and shine, but over a fairly short period shine will disappear because an oxide layer forms this protects the aluminum from oxidation and allows it to be used outdoors
• Difficult to weld
• Cracks under stress
• Requires constant annealling when being worked
• Doesn’t withstand loads well
• Melting point 650C
• Used in aircraft components, engine components and castings
25Copper 1• Easily cut and machined
• Very malleable
• Ductile
• Good conductor of heat and electricity
• Easily machined
• Corrosion resistant
26Copper 2• Can be worked cold but does work harden
• As it is work hardened it becomes harder to work with, eventually cracks appear and it can break. This can be reversed by annealing
• Can be joined via hard/soft soldering
• Used for electrical cables, central heating, printing circuits, pipes.
• Melting point 1100C
27Zinc 1• Easily worked
• Has an oxide layer which prevents oxidation
• Corrosion resistant
• Used in the galvanisation process to protect steel from rusting
• Used in products such as buckets, water tanks and car bodies to prevent rust
• Used as an element in solder fluxes
28Zinc 2• Used in die casting
• Becomes brittle when worked
• Used in batteries, die casting and galvanising
• Melting point 420C
29Stainless Steel• Steel alone when left uncoated will oxidise (rust). One way of preventing this is to alloy it with another metal.
• Stainless steel is an alloy of steel, chromium and nickel.
• Corrosion resistant
• Expensive
• Hard to cut
• Used for kitchen utensils, medical tools and chemical and nuclear industries
30Duralumin• This is an alloy of aluminium, copper and manganese.
• Lightweight and strong
• Age hardens it
• Malleable
• Ductile
• Easily machined
• Work hardens
• Used in the aviation and automobile industries
31Brass• Alloy of copper and zinc
• Corrosion resistant
• Harder than copper but can easily be joined using hard and soft soldering
• It has good heat and electrical conductivity
• Casts well
• Easy to machine
• Susceptible to cracking
• Needs to be annealed constantly
• Used in central heating valves, electrical components, ships propellers and plumbing fittings.
32Thermoplastics• Thermoplastics can be reheated, softened, shaped, reshaped and cooled many times over. They can be recovered and recycled easily.
33Thermoplastics 1• Acrylic
• HDPE (High Density polyethylene)
• LDPE (Low Density polyethylene)
• PET (Polyethylene terephthalate)
• PVC (Polyvinyl chloride)
• PP (Polypropylene)
• Compressed PS
• Expanded PS
• ABS (Acrylonitrile butadiene styrene)
34Acrylic• Stiff
• Hard
• Durable
• Can be easily scratched
• Good electrical insulator
• Brittle and can break
• Scratches easily
• Splinters easily
• Used for lighting, CD cases, car lights and baths
35HDPE (High Density polyethylene)• Good electrical insulator
• Chemical resistant
• Impact resistant
• Flexible
• Colour tends to fade over time
• Can break under stress
• Used for water tanks, pipes, buckets and bowls.
36LDPE (Low Density polyethylene)• Good electrical insulator
• Chemical resistant
• Flexible
• Colour tends to fade over time
• Can break under stress
• Used for washing up liquid bottles, Dustbin sacks, Cable insulation, Packaging film
37PET (Polyethylene terephthalate)• Good alcohol and oil barrier
• Chemical resistant
• High impact resistance
• High tensile strength
• Can discolour
• When used in containers for foodstuffs needs to be treated to prevent taste problems
• Fizzy drinks bottles
38PVC (Polyvinyl chloride)• Good chemical resistance
• Weather resistant
• Stiff
• Tough
• Hard
• Lightweight
• Can become brittle over time
• Ultraviolet light causes brittleness
• Used in electrical wiring insulation, Pipes and guttering , Floor covering
39PP (Polypropylene) 1• Light, hard
• Chemical/impact resistant
• Ultraviolet causes degradation
• Oxidation causes problems during manufacture
• Medical syringes, Carpets, Kitchenware
40PP 2• A range of colours are available
• • It takes a range of surface finishes well
• • It is a durable/strong material which is suitable for purpose
• • It has flexibility
• • It can be cleaned easily
• • Resistance to chemicals/liquids/water
• • Good impact resistance
• Suitable for mass production – injection moulding/rotational moulding
• Can be recycled when finished with
• Self-finished material
41Compressed PS• Light, hard, stiff, brittle,
• low impact strength
• Weak
• Ignites easily
• Used in CD cases, Water tanks, fridge linings
42Expanded PS• Buoyant, lightweight, good insulator
• Crumbles and breaks
• Easily ignites
• Used for Packaging and Insulation and displays
43ABS (Acrylonitrile butadiene styrene)• Chemical resistant
• Hard & Tough
• UV causes degradation
• Used for Mobile phone casings and Safety helmets
44Thermosetting Plastics 1• Epoxy resin
• Urea formaldehyde
• Polyester Resin
45Thermosetting Plastics 2• Thermosetting plastics on the other hand are produced by mixing two components, a resin and a catalyst, together. These are usually in the form of liquids or pastes.
• Unlike thermoplastics, thermosetting plastics, once shaped cannot be heated and reshaped.
• Thermosetting plastics are therefore hard to recycle.
46Epoxy Resin• Corrosion resistant
• Electrical resistant
• Good bond qualities
• Health problems
• Can cause Allergic reactions
• Used for Adhesives, Paints and coatings and Electronics
• Prepared by mixing the two parts with catalyst before being applied
47Urea formaldehyde• Strong
• Hard
• Brittle
• Heat resistant
• Easily moulded
• Water Resistant
• Can emit toxic vapors during manufacturing process
• Electrical fittings
• Domestics appliances
48Polyester Resin• Good electrical insulator
• Heat resistant
• Brittle
• Can crack
• Used for Glass reinforced boats and Garden furniture
• Polymers used are Polyester resin, Epoxy resin
49Hardwoods• Hardwoods come from bread-leaved trees whose seeds are enclosed.
• Common hardwood trees include oak, mahogany and beech, hardwood trees usually grow in warmer climates and take on average 80 - 100 years to reach maturity. Due to the relatively long time they take to grow, hardwoods tend to be more expensive than softwoods. Very often hardwoods come from inaccessible places and this also adds to the cost.
• Added to this, there is also an environmental issue. If a tree takes 100years to mature it takes a long time to replace. For this reason there is concern about the overharvesting of hardwoods.
• They produce tough, strong timber and often have a close grain.
50Hardwoods• Oak
• Mahogany
• Beech
51Oak• Strong, hard, tough
• Works well
• Durable
• Expensive and heavy
• Prone to splitting
• Can be physically hard
• Used for high quality furniture, construction and garden furniture
52Mahogany• Easy to work
• Durable
• Finishes well
• Grain can be variable
• Prone to warping
• Physical hardness varies
• Used in Furniture, Veneers and Floorboards
53Beech• Physically hard, tough
• Strong
• Has few knots
• Takes finish well
• Durable
• Has nice grain
• Polishes well
• Prone to warping
• Not suitable outside
• Difficult to work
• Workshop benches, School desks and Furniture
54Softwoods• Softwood is the wood that comes from cone-bearing conifer trees. They have needles rather than leaves.
• Examples of softwoods are Scots pine (red deal), Parana pine and whitewood.
• Softwoods grow quicker than hardwoods. On average they take 30years to mature and can be produced in plantations where they can be forested and replanted.
• As a result of careful planning, softwood is a managed resource.
As a consequence, softwoods tend to be cheaper to buy than hardwoods.
• As a rule, softwoods are easier to work than hardwoods.
55Pine• Straight grain
• Easy to work
• Knots can make working difficult
• Comes from cone bearing (conifer) trees
• Grow quickly (30 years)
• Cheaper than hardwoods
• Used in Construction, Roof joists and Floorboards and Furniture
56Composites• If two or more materials are combined together by some kind of bonding, a composite material is created.
57Glass reinforced plastics 1Glass reinforced plastics - Is a composite material that is manufactured from thermosetting plastic resin that has been reinforced using very fine glass. This glass comes in the form of either matting or in strips.
58Glass reinforced plastics 2• Can be as strong as steel
• Good strength-weight ratio
• Resistant to corrosion
• Prone to osmosis (water seeps through and delaminates the hull)
• Resin and catalyst give off harmful toxic fumes.
• Thermosetting resin reinforced with very fine glass, resin is strong(compressed) not good tensile strength and is brittle, adding glass matting improves this.
• Used for Car bodies and Boat hulls
• Gloves must be worn and must be carried out in well ventilated room.
59GRP Process• Manufacture the mould
• Apply release agent / polish / wax to the mould
• Gel coat mixed/ resin mixed
• Gel / resin coat applied
• Add / spray a layer of glass fibre
• Add a layer of resin / work resin into glass fibre layer
• Repeat for subsequent layers
• Allow to set / cure
• Remove and trim
60Carbon Fibre• Can take very heavy load
• Extremely strong, far stronger than GRP
•
• Extremely strong/durable/tough/impact resistant
• Light weight
• Good strength to weight ratio
• A uniform strength can be achieved
• High cost of material
• High wastage
• Time consuming/skilled process to manufacture
• Relatively high cost of production method
• Aircraft Sports Equipment Racing car manufacture
61MDF• Can be laminated to improve strength/ aesthetics
• Is easily workable
• No danger of splitting/ warping due to no grain
• Produces dust when worked - which is irritating towards the skin, nose and throat. Dust extraction should be used.
• Can be very heavy
• Used for Flat pack Furniture (with formica), Worktops.
62MDF ProcessMade from wood chips from wood waste which are heated and pressurised, then the pulp is adding with synthetic resins that bond the material together, making it uniform in thickness with a fine texture. After cooling, the sheet material is trimmed.
63Chipboard• Very cheap
• Easily workable
• Can become waterlogged and swell
• Unattractive, Same process as MDF, comes in normal, medium, and high-density forms. Most common is normal density. Same uses as MDF.
64ChipboardWood particles are glued together under heat & pressure. Results in a rigid board, with a relatively smooth surface. If wet can swell and break down.
65Laminate• A material that is produced by bonding together two or more layers of material. Very stable. Do not warp or misshape. Can be easier to work than wood.
66Plywood 1• Very strong and stable
• Doesn’t warp/distort
• Relatively cheap
• If damp, the the layers delaminate and come apart
• Used in Flooring/construction, Flat pack furniture, Schools workshops
67Plywood 2Manufactured from layers of veneers bonded together with the grain direction at 90 degrees to the sheet of veneer above and below it. Odd no. of sheets.
68BlockboardManufactured by softwood strips 25mm wide positioned edge-to-edge, it is then covered with an attractive veneer such as beech on either side of the sheet, it is then glued together with water based glues and subject to heat and pressure, therefore making it suitable indoors.
69Blockboard 2• Good resistance to warping/distorting
• Strong and durable same uses as plywood
• Water based glues used make it only suitable for indoor use
• Edges need finished with strips
70Makeup of Blockboard and ply
71Manmade boards over Timber• uniform thickness and quality which is not limited by the size of natural timber boards
• Manufactured boards tend to be of equal strength in all directions
• Manufactured boards do not warp/shrink/twist/cup/split as much as natural timber therefore making the boards more stable in large sizes
• The cost of manufactured boards tends to be less than natural timber making the cost of the final product lower
• Reduction of knots affecting aesthetics
• An expensive appearance can be gained by using a limited amount of expensive material
72Thermo-ceramics• Extremely hard
• Very stable at high temps
• Very strong at high temps
• Superior to ceramics
• Brittle, break when dropped
• If they are imperfections in the material, it can break/crack
• Very expensive
73Thermo-ceramics 2• They are advanced ceramic materials that are used in high temperature surroundings. They are produced by combining ceramic and metallic powders by sintering. The powders are subject to heat and pressure in a die until the particles bond.
• Used for Turbine blades in jet engines, Turbo chargers in racing cars. used in specialist engineering situations.
74Tinted glass and Photochromic glassGlass that automatically darkens when exposed to ultraviolet light & then reverts to when light has gone.
Used in spectacles.
Glass is impregnated with minute silver halide particles, which reacts to light, is encapsulated and sealed within the glass
75Solar PanelsPhotovoltaic cells, constructed from silicon have two layers: when exposed to light one layer becomes electron rich while the other is electron deficient, therefore a current is produced which can then be tapped into via contacts.
• The running costs are relatively low/cheap
• Little if any maintenance is required
• They can be used in remote areas
• No emissions are given off
• They don’t use finite/man-made resources/is sustainable
76Solar Panels 2• Extremely inefficient and uneconomical
• Limited applications as the environment must be in sunny areas that receive plenty of light
• Useful in remote places (marine buoys..etc) where mains power is not readily available.
• Marine buoys, ships,remote railway signalling
• Medicals in developing countries
• Domestic housing
77LCD 1Liquid crystals are organic, carbon based compounds that are have both liquid and solid characteristics, because of the molecular arrangement, when voltage applied, on which light falls, the crystal goes dark.
78LCD 2• Ultra flat screens
• Very high resolution
• Can harness millions of colours
• Images produced are inferior to cathode-ray televisions and screens
• Do not require much power
• Used for Portable devices (phones..etc) Computers TVs
79LCD Advantages1. Low energy requirement/efficient.
2. Extends battery life/.
3. Lightweight units
4. Thin / small / compact unit / minimal space required
5. Increased portability.
6. Produce a wide range / 256 colours.
80LCD Disadvantages1. Can be broken from a direct impact / relatively easily.
2. Limited viewing angle.
3. Expensive to replace / high maintenance cost / difficult to fix.
4. Can suffer from image persistence / retention.
5. A small damaged area can affect the whole screen.
81Electroluminescent lightingConverts electrical energy into light by applying a voltage across electrodes.
• Extremely low fuel consumption. Used for LCD displays e.g. blue glow on a digital watch.
• Very low power consumption
• Organic phosphor materials have a limited life span
• LCD backlighting Billboards Watch backlights
82Electroluminescent lighting Advantages• Low power consumption /energy efficient.
• Be powered by smaller batteries / longer battery life.
• Cheaper to run.
• Can be solar powered.
• More sustainable / eco-friendly.
• Panels are very thin.
• Can fit into small spaces / be easily incorporated into products.
• Panels can be applied to curved/ flexible products.
• They are waterproof.
• They are tough /robust /reliable.
• Need little maintenance / are long lasting.
• They do not get hot.
83Smart Materials“a material that reacts to outside stimulus, then once that stimulus has been removed, changes back into its original state
84SMAs• A material that can be deformed having had an outside stimulus and will revert to its original shape when the stimulus is removed
• change in stimulus (temperature/electricity) produces a change in shape/movement
• Can be repeated millions of times
• Expensive to produce
• Difficult to machine
• Not very strong
85NitinolThe nitinol will bend or contract until the heat source is removed, at which it will return to its original shape.
86Reactive Glass• Glass that goes dark when receives an impulse from the impregnated silver halide particles.
• Rapid transition from clear to dark.
• Very effective at what they do.
• Used in Welding masks, Privacy glass
• The glass is made with sub-microscopic particles of silver-halide
• The reaction with ultraviolet/sun light/electrical stimuli / heat Causes a chemical change in the glass
87Photochromic paint• Paints that contain pigments that change colour instantly when stimulated with UV, when the light source is removed it returns to it’s original colour
• Reversible process
• Almost instant transition of colour
• Can create stunning pigment changes
• Used in Security markers, UV warning sensors, Art
Smart action is when you apply ultra violet light / direct sunlight (Not light) it is resulting in a colour change.
88Quantum tunnelling composites (QTCs)A smart material that when stretched, compressed, twisted goes from being an electrical insulator (relaxed) to an electrical conductor (Activated), allowing current through, sometimes very high currents. As the strain increases, the material will conduct more electricity.
• Instant transition of property
• Proportional properties: Strain and conduction
• Can be used millions of times non-stop
• Used for Power tools, Robots, Textile industry.
89Nuts and bolts• Nuts are usually manufactured from mild steel or med carbon steel
• Advantage of nuts and bolts is that they can be easily undone allowing components to be replaced or repaired.
• The diameter of a bolt is always in mm and is sold in standard or stock sizes
• The most commonly used thread is the ISO metric thread (root angle 60 degrees)
• Others have different angles (British Standard Whitworth threads – 55 degrees)
90PitchThe pitch of a thread is the distance that a screw or bolt will travel through one complete revolution.
91Screwthread terminology
92V Thread• Generates a lot of friction/locks in place.
• Can be used with readily available standard components e.g. nuts.
93V Thread 1
94Acme Thread• Strength / transmits large forces.
• Applies force in both directions.
• Allows a disengaging facility / easy engagement
95Acme Thread 1
96Buttress Thread• Applies force in one direction only.
• Facilitates quick release systems / easy engagement.
97Buttress Thread 1
98Square Thread• Used for high loads
• Lowest friction and most efficient thread form
• but it is difficult to fabricate
99Square Thread 1
100Lock Nuts• Where vibration is an issue there is a danger that it could cause some nuts to come loose. In these cases lock nuts are used
• Lock nuts might have split pins put through them or nylon inserts which lock the nut as it is being tightened
101Cutting Threads in Holes (Tapping)lt is often necessary to cut a thread either into a hole, to enable a machine screw to be screwed into it, or onto a rod so that a nut can be screwed onto it.
• The tapping hole diameter is determined by subtracting the depth of the thread from the outside diameter of the bolt or machine screw.
102Cutting Threads in Holes (Tapping) 1• Once the hole is drilled the first tap, the taper, is placed into the hole and using a tap wrench the thread is carefully cut. lt is important that the thread is cut carefully.
• The wrench and tap must be slowly turned through half a turn clockwise and then a quarter of a turn anticlockwise to break off the swarf.
• The tap will gradually work through the piece of metal until it appears on the other side. During this process some lubrication should be applied. This lubrication traditionally has been tallow, but any grease or oil will work.
• This process is repeated with the intermediate tap and then finally with the plug or bottoming tap.
Must be done at right angles
103Cutting Threads in Holes (Tapping) Sizes
104Cutting threads on a rodA thread can be cut by hand or by using a metalworking lathe
• The quickest and most common way to put thread on a bar is to cut it by hand
• The tools required are a die and a die stock holder
105Cutting threads on a rod 2Firstly, the end of the bar that is to be thread needs to be slightly chamfered with a file. This will help the die to go onto the bar.
• The die then needs to be screwed onto the bar.
• The biggest problem is making sure that the die goes onto the work squarely. If this is not done a 'drunken thread' is produced. This means that any nut screwed onto the bar will not be at right angles to the bar and will appear wobbly on the bar.
106Cutting threads on a rod 3Set the work up in the chuck on the lathe and place the die between the work and the tailstock and, by hand, turn the work until the die just begins to cut. As the axes of the lathe and the tailstock are at 90" to each other, the die must go on at the correct angle.
• Once the die has started to cut the diestock should be gently turned half a turn clockwise and then a quarter of a turn anticlockwise to break off the swarf.
• As with cutting an external thread, some lubrication is again necessary.
107Cutting threads on a rod 4
108Spacers and Washers• Sometimes used in machinery.
• Used in situations where components need to be separated on a shaft, such as on a bicycle gears where it is sometimes necessary to put a spacer to separate the gears.
• Come in various materials e.g. HDPE, nylon, steel.
• Can also be used as spacers, anti-vibration devices and locking devices.
109Machine screws• Parallel sides with standard threads cut into them.
• Usually manufactured from carbon steel and are mass produced.
• Come with a variety of different heads or tops. Most common are countersunk (which allow them to fit flush with the material) heads and cheese heads (which sits above the metal into which it has been screwed).
• Common heads include Phillip’s, Star and Allen heads.
110Wood Screws• Classified first by shape of screw head and secondly by length of screw itself.
• Three types of head; Countersunk head (allow flush surface), raised head (Head is slightly domed and round head (Rests on top of the surface of wood).
• Pilot hole should be used to avoid splitting the wood.
• Wood screws are tapered, machine aren’t
111Rivets 1• Are permanent joints in metals. There are two kinds of rivets, solid rivets and pop rivets.
• Solid rivets are manufactured from soft iron because they need to be ductile and easy to work as they have to be hammered into shape.
• Pop rivets are usually manufactured from aluminium and, instead of being hammered into shape, are fixed into place using a pop rivet gun.
• Examples: Countersunk rivet, snap rivet, flat rivet, pop rivet.
112Types of Rivets
113Riveting Process
114GearsEssentially, they are used to transmit rotary motion in various ways. Gears can be used to:
• Change direction of rotary motion.
• Change spindle speeds.
• Transmit motion through 90 degrees.
If both gears were required to turn in the same direction an extra gear called an idler would be placed between the input and output gears. An idler can be of any size.
115Compound Gear TrainsFor more complex tasks, a compound gear train is used. This involves separate gear trains that mesh together. Can significantly increase or decrease the number of possible rotational speeds
116Gears Schematic Drawings
117Gear Ratio
118Spur gear• Speeds can be increased or decreased
• Direction of rotation can be changed
• Used in Simple gearboxes, Clothes dryers, Alarm clocks
119Spur Gear
120Bevel and mitre• Can have shafts at 90degrees
• Different sizes of gears can change speeds
• Commonly seen on hand drills
121Bevel and Mitre
122Worm and wheel• Transmit force and motion through 90degrees
• Reduction in rotational speed possible
• Used in food mixers
• It gives a large gear ratio / velocity ratio / increases small input force exerting a large output of force / high torque / strong pull.
• The system will not overhaul / run back when released / is self- locking so it is safe / will not drop the load.
• It is a compact / simple system compared to other systems that do a similar task therefore the unit can be made smaller / cheaper.
123Worm and Wheel
124Rack and Pinion• Used to change rotary motion into linear motion
• Used in pillar drills
• Used in steering mechanisms in cars
• A gear wheel is designed to mesh with the rack and as the gear
wheel rotates it moves the rack from side to side.
125Rack and Pinion
126Bearings• Bearings are used to reduce friction and decrease the wear of materials at their joints e.g. where a rotating shaft is being supported, so the bearings reduce friction and allow shafts to spin more efficiently.
• In its simplest form, can be a support that holds a rotating shaft.
127Plain BearingsPlain bearings
• A plain bearing in its simplest form can be a support that holds a rotating shaft.
• They are cheap
• They have less complex parts / simple to make
• They can take great loads
• They spread the load over a greater surface
• They work effectively at slow speeds.
128Bushes 1• However, because of friction the material from which the support is manufactured would soon wear down and either cause the shaft to spin inefficiently or cause a catastrophic failure of the support.
• One way of solving this problem is to place between the support and the shaft a sleeve of some kind of 'bearing material’ that has a low coefficient of friction. A sleeve of bearing material is called a bush.
129Bushes 2• The most common material for bushes is bronze, which is an alloy made up of approximately 90 per cent copper and 10 per cent tin. The disadvantage of using a bush is that they wear out over time and have to be removed and replaced. Bushes can be manufactured from other materials. For instance, nylon is increasingly used as it is a ’self-lubricating’ material and some ceramics are being used.
• A bush is better than ball bearings under heavy loading
• Bushes are cheaper than bearings
• Bushes require less maintenance than ball bearings
130Plain Bearing and Bush
131Journal bearings• The main difference is that, instead of having a bush insert, it has a layer of grease, or oil, between the rotating shaft and support. The theory is that the layer of grease, or oil, is very thick and therefore the shaft never actually comes in contact with the support. In order to keep this type of bearing working efficiently, it is important that regular servicing is undertaken and the grease is kept to the correct level. To top up the oil or grease, it is fed into the bearing under pressure through a small hole.
132Journal Bearing
133Ball bearings• Ball bearings are one of the commonest forms of bearing.
• Essentially, spherical steel balls are held in a ball race that allows the inner race to spin independently from the outer ace.
134Ball Bearing
135CamsCams are usually used in machines where, in some part of that machine, rotary motion needs to be changed into reciprocating linear motion.
136Pear Shaped CamPear-shaped cam - Used in control inlet and outlet valves in engines. Symmetrically shaped so rise and fall times are identical. Causes follower to dwell for part of its (the cam’s) rotation.
137Pear Shaped Cam
138Eccentric or Circular CamsSimplest type of cam as based on an off-centre circular disc. Smooth rise and fall. Constant acceleration and retardation. Used in fuel pumps.
139Eccentric Cam
140Heart Shaped CamsSymmetrical cams that generate continuous motion. Used in sewing machines and to wind relay coils and motor windings.
141Heart Shaped Cam
142Snail CamsGenerate output with uniform acceleration and retardation. Gives the follower a sudden drop. Uniform rise. Will only rotate in one direction
143Snail Cam
144Cams Summary
145Flat FollowerLots of friction. Cannot follow intricate contours. Has a large bearing surface, Is prone to friction/heat, Is ideal under heavy load.
146Knife FollowerProvides the most accurate conversion of movement. Can be used to follow hollow contours. Has a very small bearing surface, Provides a very accurate conversion of movement, Can be used on hollow /intricate/sharp contours, Not good under heavy load, Relatively low levels of friction
147Round FollowerLeast friction. Cannot be used to follow hollow contours. Most expensive. Cannot follow intricate/sharp contours, Can be used at high speeds
148Follower
149Scale of Production• One off - 1
• Batch 100s - 1000s
• Continous - hundreds of thousands
• Mass - Hundreds of thousands - millions
150One Off Production• Labour intensive
• Used by small specialist companies
• a skilled workforce specialist skills EG engineering
• specialist materials often required EG specialist modelling materials
• high quality products manufactured
• final products often expensive due level of skill required to manufacture them and cost of specialist materials
• a high standard of quality control
• products manufactured for as specialist market clientele
• Used for prototypes specialist models, handmade items, specialist engineering one offs.
151Batch production• Batch production often makes use of flexible manufacturing systems (FMS) to enable companies to be competitive and effective.
• The use of CIM (computer-integrated systems) involving automated machinery enables production 'downtime' to be kept to a minimum.
• Lower unit cost than one-off production.
• Scale of buying materials enable cost savings and identical batches of consistently high-quality products are manufactured at competitive costs.
• Poor planning can result in extra storage costs
152Mass Production• Makes use of efficient automated manufacturing processes and a largely unskilled workforce.
• Mass-produced products are designed to follow mass market trends, so the product appeals to a wide national and international target market.
• Product planning and QC in production enables manufacture of identical products.
• Production costs are kept as low as possible so the product will provide value for money.
• Low unit costs
• Reduced labour costs
• High set up costs expensive materials
• Inflexible – cannot respond quickly to market trends
153Continous Production• Used to manufacture standardised mass-produced products that meet everyday mass-market demand.
• The production of blow-moulded fizzy drinks bottle, for example, necessitates 24-7 to satisfy customer demands for soft drinks.
• This type of production is highly automated and uses machines that can run continuously for long periods of time with breaks only for routine maintenance.
• Reduced labour costs
• Can run 24/7
• High set up costs expensive materials
• Inflexible – cannot respond quickly to market trends as it runs 24/7
• Low unit costs lead to cheap products. (1)
• Minimal wastage due to rigorous QC systems. (1)
• Material costs can be minimized due to economies of scale / bulk buying.
154CastingCasting is the pouring, or forcing of molten metal into a cavity and then allowing the metal to cool or solidify. The 2 main types of casting is sand casting and die casting.
155Sand Casting• Once the metal has soldified the sand is broken open and the product or component is removed.
• The first step in sand casting is to make a mould in sand using a pattern. A pattern, usually manufactured from wood a medium density fibreboard (MDF is a replica of the object that is so be cast. It is identical to the finished product apart from the fact that it is slightly oversized to allow for the contraction of metal as it cools down.
• The majority of patterns are made in two parts. They are cut down the centre line and are held together using dowels. Using split patterns allows two sides of a sand mould to be created and complex casting to be produced.
156Sand Casting 1• The pattern mat be designed with sloping sides so that it can be easily removed from the mould without damaging the walls of sand.
It must have no undercuts or sharp edges and any corners must be finished off with fillet radii.
• Molten metal is poured/forced into a sand mould with a cavity where the metal fills;
• Firstly, a mould is produced by green sand (or Petrabond) with a pattern inside to create the cavity for the metal (usually in two parts, to create a complex shape) (usually made from MDF) that is slightly oversized to allow for contraction.
• The pattern is covered with parting powder (to stop it sticking) and then compact facing sand and the drag is filled with backing sand.
• The cope and drag are placed on top of one another, the sprue pins are locked in place; this is where the metal will enter the cavity, (runner) and how the air is released (riser). Gates are cut and a hollow is cut where the metal will flow into the sprue pins.
• The mould is clamped and enclosed, the metal is heated in a crucible in a furnace
157Sand Casting Advantages• Produces extremely high quality metal components
• Complex shapes can be produced
• Large shapes can be produced
• Inexpensive
• Complex shapes can be produced
• Effective / fast /cheap method of production
• Produces a strong component.
• Repeatable process
• Casting generates little waste / economic on materials.
• Low priority on dimensional accuracy / surface finish.
• Metals can be alloyed to give a range of properties
158Sand Casting Disadvantages• Is a very time-consuming, therefore not suitable for mass production, and is dangerous process
• Pattern making requires highly skilled craftsman
• Requires many different parts processes before actually casting the metal.
• Can be a cheap process; but is labour intensive.
• Sand moulds can only be used once
• Surface finish not always good
• Labour intensive
• Slow production rate
159Sand Casting applications and usesMaterials used Ferrous metals
• Aluminium Magnesium Brass Bronze Uses
• Machinery component Engine parts Mechanical pieces 70% of all metal components are made
from sand casting Caterpillar tracks
160Sand Casting
161Die Casting 1• Firstly, the mould is sprayed with lubricant to control the temperature and ease the removal of the component,
• Molten metal is then shot into the mould,
• Once filled the pressure is maintained until it has solidified and cooled.
• It is then removed by ejector pins, the gates, runners and risers are cut off.
162Die Casting 2Gravity die casting: molten metal flows into the cavity under the influence of gravity.
Pressure die casting: Dies are reusable moulds made from high-speed steel. The metal is forced into the die under hydraulic pressure.
163Die Casting Advantages• High volume process suitable for mass production
• It is highly automated
• Produces very high quality castings.
• Unlike sand casting, it cannot be done in schools.
• Produces good surface finish
• Good control over mould temperature during process
• Elements such as screw threads can be including in the casting
164Die Casting Disadvantages• High set up costs
• Long lead time
• Limited sizes possible
• Not all alloys suitable for process
• Large volume production requires to make process economical.
165Die Casting Applications and usesMetals used Non Ferrous metals:
Zinc Aluminium Copper lead
Uses
Engine blocks Large components Same as sand casting but not as complex Taps Model cars
166Die casting diagram
167Die Casting over Sand Casting• It is faster as die is reusable / you do not loose /break mould each time.
• It requires minimal labour due to automation / not re-making moulds.
• It produces finer detail / smoother/ higher quality mouldings as casting reflects a machined surface rather than sand texture as pressure is used to force the metal into the die. (1)
• It is more accurate so will require less machining.
• High level of repetitive accuracy / less prone to error due to collapsing sand mould (1)and impurities
• It is a safer process due to molten metal being enclosed within the machine / not manually poured.
168Milling and routing• It is a process of cutting away material, it can be CNC, and it works by the piece of work being fed through a rotating cutter.
• Routing is for wood; milling is for metal; and is usually used for cutting slots into material.
• The work must be securely fastened to the bench and the rotary speed and the speed the work travels through the cutter are closely controlled.
• Safety must be adhered to
169Milling and routing Advantages• Very neat and tidy process
• Depth of groove can be customised
• Relatively quick and inexpensive process
• Suitable for any production method as the initial setup costs aren’t too high
170How milling is done• Block clamped to table / clamped in machine vice
• Cutter selected / fitted into chuck / collet / onto mandrel
• Table manoeuvred into position
• Appropriate speed / feed selected
• Cutter rotates
• Block fed into cutter
• References to up milling / down milling
• Several small cuts taken
• Cutting fluid applied
171Milling Machine
172DrillingProcess of making holes using a rotating cutting tool operated by a hand drill or drilling machine
173Cutting fluidsWhen cutting, cutting fluids or lube should be used to keep drill cool and efficient
• To increase the material removal rate / drill quicker.
• To wash away cuttings.
• To lubricate the cutting action / allow smooth drilling process / reduces snatching.
• To provide a better surface finish
• To extend the life of the tool / reduce wear.
• To prevent welding of chip to tool
174Drill Bits• Flat bits — used to drill deep holes in wood.
• Forstner bits — used to drill flat-bottomed holes in wood.
• Auger bits — used to drill deep holes using a carpenter's brace.
• Countersink bits - conical drill bits, usually 90°, that when used allow a countersunk head screw to be inserted so that the head of the screw is flush with the surface of the wood or metal.
• Hole saws — saws that are circular shaped cutting rings that range from 20mm to 15Omm in diameter.
• Tank cutters — circular cutters that have an adjustable radius for cutting holes in sheet material.
175Drill Bits
176Marking OutWhen marking out for drilling it is important to establish the correct position. The best way is to either use a scriber on metal or a sharp pencil on wood to draw lines which cross where the hole is to be drilled.
When drilling into metal it is also necessary to centre punch where the hole is to be so as to guide the drill into the correct position. To prevent the tip of the drill from slipping / guides the drill and To provide an accurate start point for the drill.
177TurningTurning can be undertaken using either a metalworking centre lathe or a woodturning lathe.
The two basic processes that the lathe can perform are
• facing off, the smoothing of the end of a piece of material
• turning down, reducing the diameter of a piece of material.
Unlike most other processes, where work is securely fixed or bolted down, the work on a lathe rotates whilst it is machined.
On a metalworking centre lathe, the cutting tools are securely fixed to the lathe whereas, with a woodworking lathe, the cutting tools are held in the hand and are rested on a tool rest.
178Types of lathes
179Metal turning Lathe
180Metalworking centre latheThe metalworking centre lathe is probably the most important and versatile machine in the workshop. It can be used for a large number of tasks, from turning down diameters on metal bars to drilling holes in the centre of round material, producing tapers or producing threads on bars, among others.
181Centre Drilling 1Centre drilling is when the lathe is used to drill a hole in the end of a rod or bar along its axis.
Unlike using a drilling machine where the work is secured and the drill rotates, centre drilling involves the work rotating in the chuck with the drill held stationary in the tailstock.
182Centre Drilling 2. Before drilling the required hole, a smaller hole must be produced using a centre drill.
Once the centre drill has been used, it is changed for a twist drill and the hole completed. The hole produced by the centre drill guides the twist drill into the work. If a large hole is required it may be necessary to use a boring tool. This is similar to the cutting tool used to turn down the outside of a metal bar, but is used internally to enlarge holes. This is held in the tool post and is again controlled by hand wheels.
183Producing a screw thread using a centre latheln the school workshop, the cutting of threads is usually undertaken by hand using taps and dies.
However, external threads can be cut using a centre lathe. A cutting tool ground to the correct thread form angle is set up in the tool post and is used to cut along the bar to produce the correct thread profile on the bar.
There are two factors that are vital. Firstly, the cutting tool profile must match the thread profile required. With a metric thread this means that the angle of the tool must be 60°.
Secondly, the rate of rotation of the work must be in relation to the longitudinal cut in order to create correct thread pitch.
184KnurlingKnurling is when the lathe is used to put a pattern onto the surface of the material, for example it may be that on the end of a particular tool a textured grip is required.
This is often in the shape of a diamond pattern and is produced using a knurling tool.
The knurling tool consists of two hardened steel rollers that have the pattern to be cut engraved on them. The pattern can come in two forms, straight or diamond shaped.
As the work in the lathe rotates, the rollers on the knurling tool are pushed into the work. As the steel rollers are harder than the bar being knurled a pattern is imprinted on the bar. This operation is usually undertaken on a slow speed.
185Wood LatheThe turning process is very similar to working on the metalworking lathe except that when woodturning, tools are held in the hand against a rest and not in a tool post.
There are three basic woodturning tools:
• gouges
• chisels
• scrapers.
186Preparing for Woodturning• If turning down long pieces of timber, the corners should be planed down. If small pieces are being turned, such as bowls on a faceplate, the corners should be cut off.
• Any knots should be avoided as these can get caught by the turning tool and fly out.
• lf a long item is being turned between centres, the centre of the material should be carefully established so that when it is secured to the lathe and rotated it is not unbalanced.
• The work is held on the lathe between a driven centre, which is positioned in the headstock and a rotating centre in the tailstock. Once the work has been secured onto the machine the tool should be checked for sharpness.
• The tool post should be positioned so that the top of the turning tool is at centre height of the work. As with the metal lathe, it is important to set the correct spindle speed for the task in hand.
187Injection MouldingInjection moulding can be used for both thermoplastics and thermosetting plastics. However, because thermosetting plastics are created using resin and a catalyst, thermoplastics are the most common material used in injection moulding.
• The process involves molten plastic being injected under pressure into a mould.
• Plastic granules are placed in a hopper and then forced into a heated chamber using an Archimedean screw. The plastic is then injected into a two-part mould which is a ‘negative’ of the product required.
• The component is rapidly cooled (usually with water) and then ejected from the mould.
188Advantages and Disadvantages of injection mouldingAdvantages
• Ideal for mass production: low unit cost for each moulding for high volumes
• Precision moulding: high-quality surface finish or texture can be added to the mould
Disadvantages
• High initial set-up costs as mould expensive to develop
and produce
189Applications of Injection MouldingPolymers Used
• ABS, HDPE, Nylon, PP, PS
Uses and applications
• Casings for electronic products,
• Packaging containers
190Injection Moulding
191ExtrusionExtrusion is a manufacturing process that is used to create long products that have a particular cross section. The long component parts of unplasticised polyvinyl chloride (uPVC) window frames and rainwater gutters are examples.
• The process is very similar to injection moulding. The material is heated up in the same way and then, instead of being forced into a mould, is forced through a die of the desired cross section.
• Hollow sections can be produced by placing a pin inside the die.
192Extrusion1. Granules fed in (1)
2. Motor I motor tum screw (1)
3. Screw I screw pushes material along (1)
4. Heaters I granules is heated (1)
5. Polymer melts (1)
6. Die I mould /polymer squeezed through die (1)
7. Cooling tanks I formed shape is cooled (1)
8. Run-out support I tube is supported as it is fed out (1)
193Extrusion
194Blow mouldingBlow moulding is the process used to produce hollow products such as bottles from thermoplastics.
The first part of the blow moulding process is similar to injection moulding and extrusion.
195Blow Moulding Process• The plastic, in the form of granules, is fed into a hopper. Like injection moulding, an Archimedean spiral feeds the granules through a heated chamber.
• As the plastic is heated it begins to soften and is extruded into a hollow tube. This hollow tube is called a parison.
• The parison is then clamped in a metal mould and air pumped into it. T
• The parison inflates to the shape of the mould.
• Once the plastic has cooled the mould is opened and the bottle is ejected.
196Blow Moulding Advantages and DisadvantagesAdvantages
• Intricate shapes can be formed
• Can produce hollow shapes with thin walls to reduce
weight and material costs
• Ideal for mass production: low unit
cost for each moulding
Disadvantages
• High initial set-up costs as mould expensive to develop
and produce
197Polymers used in blow mouldingPolymers Used
• HDPE
• LDPE
• PET
• PP
• PS
• PVC
198Blow Moulding
199Vacuum formingThe vacuum forming process involves forming thermoplastic sheets into desired shapes by firstly applying heat to the plastic to make it soft and pliable so a vacuum is produced and air pressure forces the sheet of plastic around the former.
The former is a replica, made from wood, MDF or similar material, of the item that is to be produced. Once the thermoplastic has been formed it cools and is then removed.
200Vaccum Forming Process• Mould is placed on platform and lowered
• Plastic sheet is placed into machine and
clamped
• Plastic is heated
• Platform is raised
• Air is blown in to raise plastic from mould
• Air is drawn out to form plastic over mould
• Allowed to cool